This application claims priority to German Application No. 100 29 881.8, filed Jun. 16, 2000, which is herein incorporated by reference in its entirety.
1. Field of the Invention
This invention relates to a fork lift truck having a vehicle frame and lifting mechanism, with an axle body of a front axle of the fork lift fastened to the vehicle frame by at least one elastic bearing.
2. Technical Considerations
A fork lift truck with an axle body elastically connected to the vehicle frame is disclosed in DE 198 49 770 A1, herein incorporated by reference. The elastic bearing formed by an elastomeric damping element prevents the transmission of vibrations that occur in the vicinity of the axle body to the vehicle frame. In this system, there is an additional elastic bearing that connects the lifting mechanism with the axle body, as a result of which these two components are vibrationally isolated. A tilting of the lifting mechanism is also possible as a result of the elastic deformation of the additional elastic bearing. This system has the disadvantage that the elastic bearing system can lead to lateral oscillations or vibrations of the lifting mechanism and, hence, to instability of the lifting mechanism during normal operation.
Therefore, it is an object of the invention to provide a fork lift truck that has a lifting mechanism that is vibrationally isolated from the vehicle frame, and on which sufficient lateral stability of the lifting mechanism is provided.
The invention provides a vehicle in which the lifting mechanism is connected to an axle body by a non-elastic bearing or by a rigid connecting element. Thus, the lifting mechanism cannot be displaced or inclined in a lateral direction with respect to the axle body. Vibrational isolation of the lifting mechanism from the vehicle frame is provided by the elastic bearing system of the axle body on the vehicle frame. The rigid connecting element can be configured, for example, as a threaded connection or a welded connection. When the lifting mechanism is fastened to the axle body by a non-elastic bearing, for example, by a metal friction bearing, the lifting mechanism can be pivoted with respect to the axle body around an axis that runs parallel to the axle body, which corresponds to the conventional fastening system of a lifting mechanism.
There are additional advantages if the lifting mechanism is connected to the axle body by a rigid connecting element and the lifting mechanism can be inclined together with the axle body relative to the vehicle frame. When the lifting mechanism is inclined around an axis that runs parallel to the axle body, the axle body is moved along with the lifting mechanism. The lifting mechanism can be inclined around the center axis of the axle body so that the axle body does not thereby experience much, if any, translational change in position.
The elastic bearing is preferably configured so that the relative movement that occurs between the axle body and the vehicle frame during tilting of the lifting mechanism can be equalized by the elastic bearing. When the lifting mechanism tilts, there is an elastic deformation of the bearing between the axle body and the vehicle frame. There is little or no sliding movement between components, so that little or no friction-related wear occurs either. The arrangement with the rigid connection between the lifting mechanism and the axle body and with the elastic bearing between the axle body and the vehicle frame is also maintenance-free.
Each elastic bearing has at least one elastic, e.g., elastomeric, damping element. The elastic damping element prevents the transmission of oscillations and structure-borne noise between the axle body and the vehicle frame. The elastic deformability of the damping element also makes possible a slight rotation of the axle body with respect to the vehicle frame, of the type that occurs during the tilting of the lifting mechanism. Elastomeric damping elements can be conventionally manufactured easily in any desired shape and can be permanently connected with metal components using suitable conventional methods.
At least one drive unit for the traction drive of the fork lift truck can be fastened to the axle body. A hydraulic or electric wheel motor, for example, can be located on each end of the axle body. It is likewise possible to locate a mechanical drive train in the axle body. The vibrations generated by the drive unit are transmitted to the axle body, although as a result of the elastic bearing system, they are not transmitted into the vehicle frame.
Front wheels of the fork lift are also mounted on the axle body. The vibrations and impacts that occur when the truck travels over an uneven roadway are thus also transmitted to the axle body, but they are transmitted to the vehicle frame, if at all, only after they have been damped by the elastic damping element(s). In the system of the invention, the forces of gravity that act on the lifting mechanism are supported directly on the roadway via the axle body and the front wheels, i.e., these forces are not directed into the vehicle frame.
The horizontal distance between the front wheels and the lifting mechanism can be adjusted to desired requirements if the lifting mechanism is connected to the axle body in at least two positions. This type of adjustability can be made in a particularly simple manner with the use of a screw connection. For example, if the front wheels are to be provided with chains for traction in the snow, it may be necessary to increase the distance between the front wheels and the lifting mechanism.
In one advantageous embodiment of the invention, the axle body is formed by a tubular component. The tubular configuration makes it possible to achieve an equalized distribution of stresses in the axle body. Stress peaks and the resulting potential fatigue failures are thus avoided.
It is further advantageous if at least one ring-shaped axle clamp is connected with the vehicle frame, whereby at least one elastic, e.g., elastomeric, damping element is located between the axle body and each axle clamp. Preferably, a plurality of damping elements are distributed between the axle body and the axle clamp over the periphery. As a rule, there is one axle clamp on each side of the axle body connecting the axle body with the vehicle frame.
In one appropriate configuration of the invention, the axle body is made at least partly, and preferably in its entirety, of gray cast iron. The material gray cast iron has a high internal damping, so that vibrations that occur in the drive units are partly already damped by the axle body.
In one appropriate refinement of the invention, the lifting mechanism is connected to the axle body by a rigid connecting element and the lifting mechanism is connected to the vehicle frame by at least one support element that is at a distance from the axle body, such that a torque that is exerted on the axle body can be supported via the lifting mechanism and the support element on the vehicle frame. The lifting mechanism and the support element thus form a torque support for the axle body and the drive units, so that there is no need for a torque support in the form of a separate component. The torques that are exerted on the axle body during a braking process or during an acceleration process are thereby transmitted via the lifting mechanism and the support elements into the vehicle frame.
It is particularly advantageous if the support element is formed by at least one hydraulic tilting cylinder. By means of the tilting cylinder, the lifting mechanism can be tilted relative to the vehicle frame, whereby, as described above, the elastic damping elements are deformed. At the same time, the tilting cylinder(s) can be used to support the torques that are exerted on the axle body. If the tilting cylinder(s) are located on the top of the lifting mechanism, the result is a long lever arm, as a result of which the forces to be absorbed with the tilting cylinders can be minimized.